Oh no! What is this? (PART 2)

[sarah_fox]

<p>Charles, as the only difference between a light frame and a dark frame is the shutter opening, I'd say the problem is definitely from a source of light -- which could even be IR light. The back-to-back exposures would have stabilized the sensor temperatures between light and dark frames, so the dark frame would have successfully canceled out any thermal effects. Looking at it another way, if the sensor were cool when the exposure began and much warmer at the beginning of the dark frame, thermal effects would be different between light and dark frames, not resulting in effective nullification by that method of noise reduction -- hence the need for back-to-back exposures.</p>

<p>Before sending your camera in you might see if you can replicate the problem with someone else's lens on your camera or your lens on someone else's camera.</p>

<p>Whatever piece of equipment you send in, I'd type out a detailed problem description and tape it around the camera or lens. Include printouts, because they won't look at image files you place on a disc. I'd also enclose a copy of that description loosely with a cover letter in the box. Don't depend on them to contact you either by telephone or by email to discuss the problem, because the won't. They'll simply email you after they've already sent the package on its way back to you. I've had better luck, BTW, with the folks in California, compared to the folks in New Jersey. YMMV.</p>

[sarah_fox]

<p>Charles, just one other thought: You say you recently went to Yellowstone. I was recently there myself. Some volcanic ash etched a very nice Pro-1 filter on the front of my 24-105. Nasty stuff! Maybe some of it got inside your camera?</p>

[brendan_s]

<p>I'm game:<br>

We know:<br>

* no light is getting in <- so it's probably something to do with the electronics<br>

* red mark is dependent upon focal length of lens<br>

* only occurs with one lens <- this points to something in the interaction between camera and lens<br>

* only occurs for v. long exposure (30s) <- long time for small effects to accumulate<br>

* only occurs with NR on <- guess this is irrelevant.<br>

It's an IS lens, so my guess is that at 24mm the IS electronics are closer to the camera/sensor. While it's doing it's thing the IS motor is triggering pixels (electromagnetically) in the sensor. Try it with IS off? <br>

Good luck!<br>

Brendan</p>

[vdhamer]

<p>There is a posting on this on my website:<br>

http://peter.vdhamer.com/2009/04/02/red-ufos-during-long-exposures-with-canon-24-104mm-f4l-lens/</p>